Wafer alignment system

ABSTRACT

A system is provided for producing an integrated circuit using a stepper and a scanner in successive stages. Calibration data developed for the transfer of a wafer from the stepper to the scanner while maintaining the same orientation is transformed, and the transformed data is used to align a rotated wafer on the scanner.

FIELD OF THE INVENTION

The present invention relates to photolithography processes formanufacturing integrated circuits. More particularly, the inventionrelates to a method of aligning wafers for successive stepping andscanning stages of a photolithographic process.

BACKGROUND OF THE INVENTION

Photolithography is used to manufacture integrated circuits by exposinga suitably prepared wafer to light passing through a mask. The entirewafer can be exposed at once. Often, however, separate sub-areas of awafer are successively exposed in a stepping process, or a band of lightis directed synchronously across a mask and a region of a wafer in ascanning process. Alignment is critically important when multiplephotolithographic processes are used to manufacture an integratedcircuit.

Alignment refers to, among other things, the process of registering amask to a wafer. Many methods of alignment are known. In one method, awafer is carried on a fixture called a wafer stage. The wafer is indexedto the wafer stage by a notch in its periphery and the wafer stage issupported by a movable carriage. The carriage positions the wafer stageas part of stepping and/or scanning processes.

Mirrors are typically affixed to the wafer stage and as the wafer stageis moved interferometers focused on the mirrors precisely locate thewafer stage to align the wafer stage with the appropriate mask and lightsource. Typically the wafer stage is rectilinear. Therefore, only twosets of two mirrors, one set parallel to the x-axis and one set parallelto the y-axis, are required to appropriately locate the wafer stage inthe x-y plane.

An example of a photolithographic process including stepping andscanning steps is illustrated in FIGS. 1-3. In FIG. 1, a light sourceand mask are aligned to expose a first region 1 of a wafer A. In FIG. 2,the light source and mask are aligned to expose a second region 2 ofwafer A. This constitutes a two-step stepping process. A scanningprocess then commences. In the first step of the scanning process, amask is aligned with a third region 3 of wafer A, and a light sourcetraverses the mask exposing region 3 in FIG. 3.

Alignment of the masks used in the scanning process with the existingstepped regions is critical. This alignment becomes more difficult whenthe scanning process is completed on a different machine from thestepping process. Moreover, the surfaces of the mirrors used to alignthe wafer stage are not completely flat, and mirror imperfections willaffect alignment when critical dimensions are small. The mirrors,therefore, must be calibrated.

One method to accomplish this inter-machine alignment uses a calibrationwafer. According to this method, a calibration wafer is placed in afirst machine, and a calibration pattern is printed by the first machineon the calibration wafer. The actual position of the points of thecalibration pattern are carefully measured. The calibration patternmeasurement data, along with the position of the calibration waferaccording to the alignment mirrors of the first machine, is stored in amemory.

The calibration wafer is placed in the second machine in the sameorientation as the first machine. A nominally identical calibrationpattern is printed by the second machine on the calibration wafer. Theactual position of the points of the second calibration pattern arecarefully measured. The second calibration pattern measurement data,along with the position of the calibration wafer according to thealignment mirrors of the second machine, is stored in a memory.

The first calibration pattern measurement data, first alignment mirrorposition, second calibration pattern measurement data and secondalignment mirror position are processed to account for, among otherthings, the disparities of the alignment mirrors. When a productionwafer is processed in a first machine, then transferred to a secondmachine in the same orientation, the processed data from the calibrationprocess is used to adjust the position of the production wafer in thesecond machine to bring it into true alignment with the regions exposedon the production wafer by the first machine.

When scanning is done in the same linear direction as stepping, once thewafer is placed in the apparatus, its only movement will be along the xand y axes and no rotation to change wafer orientation is necessary. Forinstance, in FIG. 10, a shallow, rectangular first region 1 a is exposedon a wafer C, followed by a similar second region 2 a as shown in FIG.11. These stepping processes could be followed by one scanning processsimilar to those shown in FIG. 3. Sometimes, however, it is advantageousto carry out stepping and scanning processes in different directionswith respect to a wafer. For example, as shown in FIG. 12, under certaingeometries a single pass of the scanner 200 in a direction 90° to thepath of the stepper 100 can expose a single region 3 a covering bothregions 1 a and 2 a.

Many integrated circuit manufacturing centers are not equipped toexecute stepping and scanning in different directions. In thesemanufacturing centers, the wafer must be rotated 90° to accommodatestepping passes orthogonal to scanning passes. This is illustrated inFIG. 13, where the wafer C has been rotated 90° to accommodate a region4 a scanned in the same linear direction as the stepping processes. Whenmulti-directional stepping and scanning requires a rotation of a wafer,the alignment process described above cannot be used. What is requiredthen, is a method of aligning and manufacturing a rotated productionwafer.

SUMMARY OF THE INVENTION

The invention concerns a method for aligning wafers in machines used tomanufacture integrated circuits.

In the invention, a first pattern is formed in a calibration wafer in afirst orientation in a first machine and a second pattern is formed inthe calibration wafer in said first orientation in a second machine.Next, the difference between the first pattern and the second pattern ismeasured and stored in a memory. The difference is transformed toaccount for a change in orientation, typically a 90° rotation.

Next, regions in a production wafer in the first orientation areprocessed in the first machine and the location of the production waferin the first machine is determined.

The production wafer is then transferred to the second machine in asecond orientation, typically at a 90° rotation.

The location of the production wafer in the second machine is determinednext, and then adjusted using the transformed difference. Finally, theproduction wafer is aligned in the second machine using the adjustedlocation data; and the regions in the production wafer are processed inthe second machine.

In one example of the invention, the first machine is a stepper and thesecond machine is a scanner, each with their own processor and memory.The scanner processor retrieves the coordinates of the cruciformpatterns, transforms them, and adjusts the alignment of the productionwafer in the scanner using the transformed coordinates.

A 90° change in the orientation of the production wafer is useful whentwo successive regions of the production wafer are exposed in thestepper in a first direction, the scanning breadth of the scannerexceeds the length of the two successive stepped regions in the firstdirection, and a single scanning pass in a second direction exposes bothsuccessive stepped regions in the production wafer in a single scanningpass.

According to one aspect of the invention, positional differences may betransformed by switching the x-coordinates of the cruciform pattern inthe scanner with the y-coordinates of the cruciform pattern in thescanner.

The above and other advantages and features of the invention will bemore readily understood from the following detailed description of theinvention which is provided in connection with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a wafer with a first stepped area exposed.

FIG. 2 is a plan view of the wafer of FIG. 1 with a second stepped areaexposed.

FIG. 3 a plan view of the wafer of FIGS. 1 and 2 with a first scannedarea exposed.

FIG. 4 is a partial schematic drawing of a stepper and a scanner.

FIG. 5 is a plan view of a calibration wafer with a nominal cruciformpattern.

FIG. 6 is a plan view of a calibration wafer with an actual cruciformpattern formed in a stepper.

FIG. 7 is a plan view of a calibration wafer with a second actualcruciform pattern formed in a scanner.

FIG. 8 is a plan view of a portion of the calibration wafer of FIG. 6and FIG. 7.

FIG. 9 is a flow chart for an integrated circuit manufacturing processincluding stepping and scanning.

FIG. 10 is a plan view of a wafer with a first stepped area exposed.

FIG. 11 is a plan view of a wafer with a second stepped area exposed.

FIG. 12 is a plan view of a wafer with a single scanned area exposed.

FIG. 13 a plan view of a wafer rotated to accommodate a single scanningprocess.

FIG. 14 is a partial schematic drawing of a stepper and scanner whereina production wafer is rotated when transferred from the stepper to thescanner.

FIG. 15 is a flow chart for an integrated circuit manufacturing processwherein a wafer is rotated when transferred from a stepper to a scanner.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

As shown in FIG. 4, a calibration wafer 10 is placed in a wafer stage112 of a first, or reference machine, in this case, the stepper 100. Thewafer stage 112 of the stepper 100 is supported by a carriage (notshown). The carriage is capable of moving the wafer stage in the x and ydirections, as indicated by the arrows 12. The wafer stage 112 has anx-location mirror 114 attached to a side 115 parallel to the y-axis anda y-location mirror 116 attached to a side 117 parallel to the x-axis.An x-location interferometer 118 focused on the x-location mirror 114 isattached to the frame (not shown) of the stepper 100, and a y-locationinterferometer 120 also attached to the frame, is focused on they-location mirror 116. The movement and location of the wafer stage isvery precisely controlled.

As shown in FIG. 5, a cruciform pattern 14 is printed on the calibrationwafer 10 consisting of points arranged in a vertical bar 16, a nominallystraight line parallel to the y-axis, and a horizontal bar 18, anominally straight line parallel to the x-axis. This pattern is producedby moving the wafer stage 112, under a light source (not shown) focusedat a non-moving point on the surface of the calibration wafer 10. Thewafer stage 112 is then incrementally traversed through the range of thecarriage in the y-direction while holding a single position of thecarriage in the x-direction as indicated by the x-locationinterferometer 118 reading of the x-location mirror 114. Next, the waferstage 112 is incrementally traversed throughout the range of thecarriage in the x-direction while holding a single position of thecarriage in the y-direction as indicated by the y-locationinterferometer 120 reading of the y-location mirror 116. Because themirrors are not perfectly flat the actual cruciform pattern 14 aproduced will be slightly curved as shown in FIG. 6.

The actual positions of the points along the nominally cruciform pattern14 a formed on the calibration wafer 10 are precisely determined usingthe stepper metrology. The x and y coordinates of these pointsconstitute an array, x_(A), y_(A)={x_(A1), y_(A1), x_(A2), y_(A2),x_(A3), y_(A3) . . . x_(An), y_(An)}. Returning to FIG. 4, this array ofpoints is transmitted by the processor 122 of the stepper 100 to itsmemory 123.

The calibration wafer 10 is removed from the wafer stage 112 of thestepper 100 and is placed in the wafer stage 212 of the scanner 200.During this transfer step, the calibration wafer 10 is maintained in thesame orientation in the x-y plane with the notch 11 of the wafer 10facing right. A second nominally cruciform pattern 14 b is printed onthe calibration wafer 10 in the same manner as the pattern 14 a wasformed on the stepper 100. The second actual cruciform pattern 14 b isalso curved and is shown in FIG. 7. The first actual cruciform pattern14 a is omitted from FIG. 7 for clarity.

The actual positions of the points along the second nominally cruciformpattern 14 b formed on the calibration wafer 10 are then preciselydetermined using the scanner metrology. The x and y coordinates of thesepoints constitute an array, x_(B), y_(B)={x_(B1), y_(B1), x_(B2),y_(B2), XB₃, y_(B3) . . . x_(Bn), y_(Bn)}. This array is transmitted bythe processor 222 of the scanner 200 to its memory 223.

The coordinates of the array x_(A), y_(A) stored in the stepper memory123 are transmitted to the scanner memory 223 by any of a number ofmeans known in the art. A calibration array is then calculated by thescanner processor 222 using the difference between the actual cruciformpattern 14 a produced by the stepper 100 and the actual cruciform 14 bpattern produced by the scanner 200. This difference is the aggregatedifferences in the actual positions of corresponding locations on thex-axis for each point on the vertical bar 16 of the cruciform pattern 14and the actual positions of corresponding locations on the y-axis foreach point on the horizontal bar 18 of the cruciform pattern 14.

To illustrate this calculation, FIG. 8 is a top view of an enlarged partof the calibration wafer showing the part of the vertical bars 16 a, 16b of the superimposed actual cruciform pattern 14 a of the stepper 100and the actual cruciform pattern 14 b of the scanner 200. For eachincremental position on the vertical bar 16, the horizontal distancebetween the corresponding points on the cruciform pattern is calculated.For example, for position y₁, shown in FIG. 8, the horizontal distancex_(A1)-x_(B1) between corresponding points of the actual cruciformpattern 14 a of the stepper 100 and the actual cruciform pattern 14 b ofthe scanner 200 is calculated. This calculation is repeated for eachincremental position on the vertical bar 16, and is assembled into thevertical component of the calibration array (x_(A)-x_(B)),y=(x_(A1)-x_(B2)), y₁, (x_(A2)-x_(B2)), y₂, . . . (x_(An)-x_(Bn)),y_(n). This vertical calibration array accounts for the difference inprofile between the x-location mirror 114 of the stepper 100 and thex-location mirror 214 of the scanner 200.

Similarly, for each incremental position on the horizontal bar, thevertical distances between the corresponding points in the cruciformpatterns are calculated, and are assembled into the horizontal componentof the calibration array x, (y_(A)-y_(B))={x₁, (y_(A1)-y_(B1)), x₂(y_(A2)-y_(B2)), . . . x_(n) (y_(AN)-y_(BN))}. The horizontalcalibration array component accounts for the difference in profilebetween the y-location mirror 116 of the stepper 100 and the y-locationmirror 216 of the scanner 200. The complete calibration array(x_(A)-x_(B)), y, x (y_(A)-y_(B)) includes both the vertical andhorizontal components.

During the manufacture of an integrated circuit according to thestepping and scanning pattern of FIGS. 1-3, the calibration array isused to determine and control the position of a production wafer 22 inthe integrated circuit manufacturing center of FIG. 4, as follows: Theproduction wafer 22 is placed in the wafer stage 112 of the stepper 100.The wafer stage 112, light source, lens, and mask are aligned to produceregion 1 and region 1 is exposed. During alignment, location data forthe wafer stage 112 is obtained using the alignment mirrors 114, 116 andinterferometers 118, 120 of the stepper. The wafer stage location isprocessed by the processor 122 of the stepper 100, and is stored inmemory 123. After exposure of region 1, the wafer stage 112 moves toregion 2 and the mask is aligned and region 2 is exposed.

For the next layer, the production wafer 22 is removed from the stepper100 and placed in the wafer stage 212 of the scanner 220. During thistransfer step, the production wafer 22 is maintained in the sameorientation in the x-y plane. The wafer stage 212, light source, lensand mask of the scanner are aligned in order to commence scanning ofregion 3 of the production wafer. In order for scanned sub-area 3 toalign with sub-areas 1 and 2 previously produced, the scanner processor222 transforms the location data obtained from the stepper 100 using thecalibration array according to mathematical models known in the art, andthe scanner 200 locates the wafer stage 212 according to the transformedlocation data using the alignment mirrors 214, 216 and interferometers218, 220. The transformed location data used to align wafer stage 212accommodates the imperfections of the location mirrors of the waferstages of the stepper 100 and scanner 200. By using the transformedlocation data the wafer stage 212 can be correctly positioned so thatthe scanning process aligns with the previously exposed regions from thestepping process.

This manufacturing process may be illustrated using the flow chart setforth in FIG. 9. A production wafer 22 is placed in the wafer stage 112of stepper 100 at step 400. Next, the location of the wafer stage isdetermined using the interferometers 118, 120 and mirrors 114, 116 ofthe stepper 100 at step 402. This location data of the wafer stage 112of the stepper constitutes stepper array x_(PA), y_(PA). The stepperlocation array x_(PA), y_(PA) is processed by the processor 122 at step404 and stored at the stepper memory 123 at step 406. At step 408, thephotolithographic manufacturing process of the stepper 100 is completed.At step 410, the production wafer 22 is transferred from the wafer stage112 of the stepper 100 and placed in the wafer stage 212 of the scanner200. During this transfer step, the production wafer 22 maintains thesame orientation in the x-y plane. In FIG. 4 this orientation is withthe notch 23 facing up.

In order to align the wafer stage 212 in the scanner 200, the stepperlocation array x_(PA), y_(PA) of the wafer stage 112 of the stepper 100is transformed by the calibration array. Specifically, the scannerprocessor 222 retrieves stepper location array x_(PA), y_(PA) from thememory 223 at step 412 and retrieves the calibration array from thememory 223 at step 414. At step 416, the calibration array(x_(A)-x_(B)), y, x, (y_(A)-y_(B)) is used to transform the stepperlocation array x_(PA), y_(PA) to produce a scanner location array x_(PB)y_(PB). The scanner location array x_(PB), y_(PB) is used to align thewafer stage 212 of the scanner 200 in step 420. The scanner 200completes its photolithographic manufacturing process at step 422.

Under the improved alignment method for accommodating rotated wafersduring the manufacture of an integrated circuit, an existing calibrationarray obtained using a calibration wafer 10 that is not rotated, ismodified and used to determine and control the position of a productionwafer 23 that is rotated when transferred from a stepper to a scanner.As shown in FIG. 14, the production wafer 23 is placed in the waferstage 512 of the stepper 500 with its notch 24 facing in a firstdirection (x). The wafer stage 512, light source, lens, and mask (notshown) are aligned to produce sub-area 1 and sub area 1 is exposed asshown in FIG. 10. During alignment, location data x_(NA), y_(NA) for thewafer stage 512 is obtained using the alignment mirrors 514, 516 andinterferometers 518, 520 of the stepper 500. This location is processedby the processor 522 of the stepper 500 at step 504 and transmitted tothe stepper memory 523. After exposure of sub-area 1, the wafer stage512 moves to sub-area 2 and the mask is aligned and sub-area 2, FIG. 11,is exposed.

For the next layer, after other processes, the production wafer 23 isplaced in the wafer stage 612 of the scanner 620. During this step, theproduction wafer 23 is rotated 90° in the x-y plane, so that its notch24 faces in a second direction (y), to accommodate a single scanningpass. In the illustrated embodiment, the second direction (y) isorthogonal to the first direction (x). The present invention should notbe limited, however, to the preferred embodiments shown and described indetail herein. Because of the rotation of the production wafer 23, thecalibration array obtained with a calibration wafer that was not rotatedis modified by switching the sub-array x_(B) for the sub-array y_(B).Substituting y_(B) for x_(B) in the vertical component of thecalibration array, (x_(A)-y_(B)), y, accounts for the difference inprofile between the x-location mirror 514 of the stepper 500 and they-location mirror 616 of the scanner 600. Similarly, substituting x_(B)for y_(B) in the horizontal component of the calibration array, x,(y_(A)-x_(B)), accounts for the difference in profile between they-location mirror 516 of the stepper 500 with the x-location mirror 614of the scanner 600. These modifications effect a switch of the verticalbar 16 a with the horizontal bar 18 b of the actual cruciform patternproduced in the calibration wafer 10 by the scanner 600. The complete,modified calibration array is represented by (x_(A)-y_(B)), y, x,(y_(A)-x_(B)).

The wafer stage 612, light source, lens and mask of the scanner 600 arealigned to commence scanning of sub-area 3 of the production wafer. Inorder for scanned sub-area 3 to align with sub-areas 1 and 2 previouslyproduced, the scanner processor 622 transforms the location data x_(NA),y_(NA) obtained from the stepper 500 using the modified calibrationarray and mathematical models known in the art. Then the transformedlocation x_(NB), y_(NB) data is used by the scanner 600 to locate thewafer stage 612 according to the transformed location data x_(NB),y_(NB) using the alignment mirrors 614, 616 and interferometers 618,620. The transformed location data x_(NB), y_(NB) correctly locates thewafer stage 612 so that the scanning step aligns with the previouslyexposed areas from the stepping process.

Referring now to FIG. 15, a production wafer 23 is placed in the waferstage 512 of stepper 500 at step 800. Next, the location of the waferstage is determined using the interferometers 518, 520 and mirrors 514,516 of the stepper 500 at step 802. This location data of the waferstage 512 of the stepper 500 constitutes an array x_(NA), y_(NA). Thestepper location array data x_(NA), y_(NA) is processed by the processor522 of the stepper 500 at step 804 and is stored in memory 523 at step806. At step 808, the photolithographic manufacturing process of thestepper 500 is completed. At step 810 a, the production wafer 23 isremoved from the wafer stage 512 of the stepper 500, rotated 90° at step810 b and placed in the wafer stage 612 of the scanner 600 at step 810c. In FIG. 14, the orientation of the production wafer 23 changes fromthe notch facing in the first direction (x) in the stepper 500 to facingin the second direction (y) in the scanner 600.

To align the wafer stage 612 in the scanner 600, the location datax_(NA), y_(NA) of the wafer stage 512 of the stepper 500 is transformedby the modified calibration array. Specifically, the scanner processor622 retrieves the stepper location array data x_(NA), y_(NA) from thememory 623 at step 812 and retrieves the modified calibration array fromthe memory 623 at step 814. At step 816, the modified calibration array(x_(A)-y_(B)), y, x, (y_(A)-x_(B)) is used to transform the stepperlocation array x_(NA), y_(NA) to produce a scanner location sub-arrayx_(NB), y_(NB). The scanner location array data x_(NB), y_(NB) is usedto align the wafer stage 612 of the scanner 600 in step 820. The scanner600 completes its photolithographic manufacturing process at step 822.

The invention provides a method of transforming calibration data toaccommodate the rotation of production wafers in successive stepping andscanning stages in the manufacture of integrated circuits. Variations ofthe disclosed embodiment will be readily apparent to those skilled inthe art. For instance, different stepping and scanning processes couldbe used to practice the invention and different mathematicalnomenclature could be used. In addition the various processors andmemory devices could be distributed differently than the components ofthe manufacturing center described. Accordingly, it is to be understoodthat although the present invention has been described with reference toexemplary embodiments, various modifications may be made withoutdeparting from the spirit or scope of the invention which is definedsolely by the claims appended hereto.

What is claimed as new and desired to be protected by Letters Patent of the United States is:
 1. A method of transforming calibration data in a wafer production apparatus, said method comprising the steps of: acquiring calibration data representative of an alignment of a second pattern having been formed on an upper surface of a calibration wafer within a second machine, with respect to an alignment of a first pattern having been formed on the upper surface of the calibration wafer within a first machine, said calibration data obtained by determining first coordinates along said first pattern and second coordinates along said second pattern on said calibration wafer; and measuring the difference between said first coordinates of said first pattern and said second coordinates of said second pattern for establishing processing pattern alignment of a production wafer in the second machine after processing the production wafer in the first machine.
 2. The method of claim 1, further comprising rotating the production wafer for processing in the second machine with respect to a processing orientation of the wafer in the first machine.
 3. The method of claim 2, wherein said rotation of said production wafer is 90°.
 4. The method of claim 1, wherein said first coordinates are x-coordinates and said second coordinates are y-coordinates.
 5. The method of claim 1, wherein the first pattern and the second pattern are formed by printing under light.
 6. The method of claim 1, wherein the calibration data is obtained using scanning metrology.
 7. A method of aligning a production wafer comprising the steps of: forming a first pattern on an upper surface of a calibration wafer in a first machine and forming a second pattern on the upper surface of the calibration wafer in a second machine; acquiring calibration data by measuring an alignment of the second pattern formed on the calibration wafer with respect to an alignment of the first pattern formed on the calibration wafer; transforming said calibration data to account for a change in alignment of said calibration wafer from said first machine to said second machine; measuring the location of a production wafer in said first machine; transferring the production wafer to said second machine, the production wafer being in a different orientation in said second machine than in said first machine; and adjusting the location of said production wafer using said transformed calibration data.
 8. The method of claim 7, wherein said production wafer is rotated 90° in said second machine with respect to the position of said production wafer in said first machine.
 9. The method of claim 7, wherein said first machine is a stepper, and said second machine is a scanner.
 10. The method of claim 9, further comprising the step of storing said transformed calibration data in said first machine.
 11. The method of claim 10, wherein said second machine uses said transformed calibration data to adjust the alignment of the production wafer.
 12. The method of claim 11, wherein two successive areas of the production wafer are exposed in the stepper.
 13. The method of claim 7, wherein the first pattern and the second pattern are formed by printing under light.
 14. The method of claim 7, wherein the calibration data is obtained using scanning metrology.
 15. A method of aligning a production wafer comprising the steps of: forming a first pattern on an upper surface of a calibration wafer in a first machine and forming a second pattern on the upper surface of the calibration wafer in a second machine; calibrating the second pattern to the first pattern; transforming the data from said calibration; determining a location of a production wafer in the first machine; transferring the production wafer to the second machine; and aligning the production wafer in the second machine in relation to the location of the production wafer in the first machine using said transformed data.
 16. The method of claim 15, wherein an orientation of the production wafer in the second machine is rotated 90° with respect to an orientation of the production wafer in the first machine.
 17. The method of claim 15, wherein said first machine is a stepper, and said second machine is a scanner.
 18. The method of claim 15, further comprising the step of storing said transformed calibration data in said first machine.
 19. The method of claim 18, wherein said second machine adjusts the location of the production wafer using the transformed data from the calibration.
 20. The method of claim 15, wherein the first pattern and the second pattern are formed by printing under light.
 21. The method of claim 15, wherein the calibration data is obtained using scanning metrology.
 22. A method of aligning wafers in machines used to manufacture an integrated circuit, comprising the steps of: measuring a difference in location from a first pattern formed on an upper surface of a calibration wafer in a first machine to a nominally identical location in a second pattern formed on the upper surface of the calibration wafer in a second machine wherein the calibration wafer is desirably maintained in a same orientation in each machine; transforming said difference in said locations to account for a change in wafer orientation from one machine to the other; measuring the location of a production wafer in the first machine; transferring the production wafer to the second machine, the production wafer being in a different orientation in the second machine than in the first machine; and adjusting the location of the production wafer in the second machine using said transformed difference in locations.
 23. The method of claim 22, wherein said difference is measured by comparing the first pattern and the second pattern formed on the calibration wafer by the respective first machine and second machine.
 24. The method of claim 23, wherein each of the first pattern and the second pattern is a cruciform shape.
 25. The method of claim 22, wherein said calibration wafer is mounted in a wafer stage and said location of the calibration wafer is determined by measuring the location of the wafer stage.
 26. The method of claim 25, wherein the wafer stage has mirrors, and the location of the wafer stage is measured using interferometers mounted in said first and second machines.
 27. The method of claim 22, wherein said first machine is a stepper.
 28. The method of claim 22, wherein said second machine is a scanner.
 29. The method of claim 25, wherein two successive areas of the production wafer arc exposed in the stepper.
 30. The method of claim 28, further comprising the step of storing said transformed difference in said stepper.
 31. The method of claim 30, wherein said stepper uses said transformed difference to adjust the location of the production wafer.
 32. The method of claim 22, wherein the first pattern and the second pattern are formed by printing under light.
 33. The method of claim 22, wherein calibration data is obtained using scanning metrology.
 34. A method of manufacturing an integrated circuit, comprising the steps of: forming a first cruciform pattern on an upper surface of a calibration wafer in a first orientation in a first machine; forming a second nominally identical cruciform pattern on said upper surface of said calibration wafer in said first orientation in a second machine; measuring the difference between said first cruciform pattern and said second cruciform pattern; storing said difference in a memory; transforming said difference to account for a change in orientation of a production wafer transferred between said first machine and said second machine; processing sub-areas on a production wafer in said first orientation in said first machine; determining the location of said production wafer in said first machine; transferring said production wafer to said second machine in a second orientation; adjusting said location using said difference; aligning said production wafer in said second machine using said adjusted location data; and processing sub-areas on said production wafer in said second machine.
 35. The method of claim 34, wherein said first machine is a stepper and said second machine is a scanner.
 36. The method of claim 34, wherein said second orientation is rotated 90° from said first orientation.
 37. The method of claim 36, wherein two successive areas of the production wafer are exposed in the stepper.
 38. The method of claim 34, wherein said difference is transformed by determining coordinates of the first cruciform pattern and the second cruciform pattern.
 39. The method of claim 35, further comprising storing data from said transformed difference in said stepper.
 40. The method of claim 39, wherein said stepper uses said stored data to adjust the alignment of the production wafer.
 41. The method of claim 38, wherein said difference is the array (x_(A)-x_(B)), y, x, (y_(A)-y_(B)), and said transformed difference is represented by the array (x_(A)-y_(B)), y, x, (y_(A)-x_(B)).
 42. The method of claim 34, wherein the first cruciform pattern and the second cruciform pattern are formed by printing under light.
 43. The method of claim 34, wherein calibration data is obtained using scanning metrology.
 44. A system for transforming calibration data in a wafer production apparatus, said system comprising: a device for acquiring calibration data representative of the alignment of a second pattern formed on an upper surface of a calibration wafer in a second machine with respect to an alignment of a first pattern formed on the upper surface of the calibration wafer in a first machine; and a device for measuring a difference between first coordinates of said first pattern with second coordinates of said second pattern.
 45. The system of claim 44, wherein the first pattern and the second pattern are formed by printing under light.
 46. The system of claim 44, wherein the calibration data is obtained using scanning metrology.
 47. A method of aligning a production wafer comprising the steps of: acquiring a first set of calibration points from a first pattern formed on the upper surface and within the periphery of a calibration wafer in a first machine; acquiring a second set of calibration points from a second pattern formed on the upper surface and within the periphery of said calibration wafer in a second machine; determining the positional relationship between said first set of calibration points and said second set of calibration points of said calibration wafer; using said positional relationship to form a calibration array representing a deviation in alignment of said calibration wafer between said first machine and said second machine; and using said calibration array to align a production wafer during processing and transfer from said first machine to said second machine.
 48. The method of claim 47, wherein said calibration array is formed by measuring the difference between said first set of calibration points and said second set of calibration points. 